The field of Augmentative Communication Technology (ACT) pertains to the application of technology to the problem of facilitating communication by individuals whose own abilities are not sufficient to allow them to communicate successfully. ACT devices may therefore be understood as "communication prostheses" for individuals with communication disabilities. State of the art ACT devices employ computer and data processing technology to facilitate communication. In general these devices receive input from the user and translate that input into an output message which approximates the message which the user wishes to communicate. Known technology allows messages to be provided in a number of forms, including visual displays and synthesized speech.
A goal in the field of ACT is to increase the rate of communication attainable through ACT devices by reducing the amount of input which is required to produce a desired message. This goal has been pursued to date primarily through the development of user interfaces which employ coding systems to invoke desired messages. In such devices, the ACT device produces output which is associated with a code supplied by the user. For example, a device may associate the code "greeting" with the message "Hello, my name is Jeff." Thus, when supplied with the input code "greeting", the device will produce the code's associated message.
A number of coding systems are currently employed by ACT devices. A first type of coding system employs fixed codes which correspond to output messages which may be produced by the system. Various fixed code schemes use truncated words, words without vowels, contractions, or sequences of graphic characters as input codes. For example, in a fixed code system, input consisting of an "apple" icon followed by a "building" icon may represent the word "school". Coding systems may also use input comprising combinations of icons and letters.
Fixed code systems generally require the user to input the full code which corresponds to a desired output message. However, some fixed code systems utilize simple predictive algorithms to present the user with a variety of input choices based on the input of a partial code. In one such scheme known as "word prediction", the user provides a truncated input code and the device displays one or more numbered "candidate" words which may correspond to the full input word intended by the user. Completion of code input is accomplished by the user's selection of the number corresponding to the proper candidate word. Similarly, in icon based coding systems, the input of a first icon of an icon sequence may produce a display of a grid of additional icons which are known by the system to follow the first icon in various input codes.
An alternative coding system employed in some ACT devices is known as variable coding. Variable coding systems are distinguished from fixed coding systems in that codes are not strictly associated with a fixed message. Rather, the message associated with a code may vary depending upon factors such as the frequency or recency of use, or the probable grammatical category of the message. Thus the hierarchy of messages and codes in a variable system is optimized by the system to correspond to the user's history of use.
As an alternative to coding systems, some ACT devices employ databases containing output messages and associated search attributes. The characteristics of a desired output message are indicated by the user in the form of a search string. The device then produces a list of messages having the attributes indicated by the search string, from which the user may select a message for output.